NUC194

Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [(PUBMED:3291115)]:

Protein kinase function is evolutionarily conserved from Escherichia coli to human [(PUBMED:12471243)]. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation [(PUBMED:12368087)]. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [(PUBMED:15078142)], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [(PUBMED:15320712)].

This is domain B in the catalytic subunit of DNA-dependent protein kinases.

Insights into the evolution of the nucleolus by an analysis of its protein domainrepertoire.

Bioessays. 2004; 26: 567-81

Display abstract

Recently, the first investigation of nucleoli using mass spectrometry led to the identification of 271 proteins. This represents a rich resource for acomprehensive investigation of nucleolus evolution. We applied a protocol for theidentification of known and novel conserved protein domains of the nucleolus,resulting in the identification of 115 known and 91 novel domain profiles. Thephyletic distribution of nucleolar protein domains in a collection of completeproteomes of selected organisms from all domains of life confirms thearchaebacterial origin of the core machinery for ribosome maturation andassembly, but also reveals substantial eubacterial and eukaryotic contributionsto nucleolus evolution. We predict that, in different phases of nucleolusevolution, protein domains with different biochemical functions were recruited tothe nucleolus. We suggest a model for the late and continuous evolution of thenucleolus in early eukaryotes and argue against an endosymbiotic origin of thenucleolus and the nucleus. Supplementary material for this article can be foundon the BioEssays website athttp://www.interscience.wiley.com/jpages/0265-9247/suppmat/index.html.